The invention relates to a device for axially conveying fluids.
In particular, less stable multiple-phase fluids which can undergo irreversible changes caused by an energy input, such as in the case of emulsions and dispersions, can run into unstable ranges in a disadvantageous manner when being conveyed in corresponding devices such as pumps.
Blood is a particularly sensitive fluid system. This opaque red body fluid of the vertebrates circulates in a self-enclosed vessel system where rhythmic contractions of the heart press the blood into various areas of the organism. In this case, the blood transports the respiratory gases oxygen and carbon dioxide as well as nutrients, metabolic products and endogenous active ingredients. The blood vessel system including the heart is hermetically isolated from the environment so that, in a healthy organism, the blood does not undergo any changes, except for the material exchange with the body cells, when it is pumped through the body by way of the heart.
It is known that, when blood comes into contact with non-endogenous materials or as a result of the effect of energy from an external source, it has a tendency to hemolysis and clot formation. Clot formation can be fatal for the organism because it can lead to blockage in the extensive branching profile of the vessel system. Hemolysis describes the condition where the red blood cells are destroyed within the body beyond the physiological dimension.
The causes for hemolysis can be of a mechanical or metabolic nature. Increased hemolysis causes multiple organ damage and can lead to a person's death.
On the other hand it is evident that it is possible in principle, under certain prerequisites with reference to constructive aspects, to support the pumping capacity of the heart or even to replace the natural heart with a synthetic one. However, a continuous operation of implanted heart supporting systems or synthetic hearts is presently only possible with certain limitations because the interactive effects of these artificial products with the blood and the entire organism still always lead to disadvantageous changes of the blood and the organism.
In the state of the art, axial blood pumps are known which mainly consist of a cylindrical tube in which a conveying part, which is executed as a rotor of an externally located motor stator, rotates. The rotor which is provided with a so-called blading, conveys the fluid in an axial direction after it has been made to rotate. The bearing of these so-called axial pumps represents a major problem. A purely mechanically bearing is disadvantageous with regard to blood damage and also the relatively high friction levels. And the magnet bearing variants as described up to the present have not, in particular, led to any satisfactory solution for the bearing conditions in axial pumps.
In the WO 00/64030 a device for the protective conveying of single- and multiple phase fluids is described whose conveying part is exclusively magnetically bearing-located. For this purpose, permanent magnetic bearing elements for the magnet bearing-location as well as permanent magnetic elements for the functionality as a motor rotor of an electromotor are preferentially integrated in the conveying part. The use of a magnet bearing for the conveying facility as described here makes it possible to waive bearing elements normally arranged in the flow current of the fluid to be conveyed which lead to dead water zones and vorticities of the fluid to be conveyed and, subsequently, have a negative influence on the current flow.
The magnetic bearing described here accommodates both the axial as well as the radial forces. The axial location of the conveying part is actively stabilised whereas the radial bearing of the conveying part is effected exclusively passive by means of the existing permanent magnets. However, the conveying facility as described has several disadvantages.
The passive magnetic radial bearing is characterised by relatively low rigidity and dampening where, during the pumping action, problems occur when passing through critical speeds of the rotor and/or the bearing. Possibly existing hydrodynamic and mechanical imbalance of the rotor has serious effects on the function of the pump, particularly when used as a blood-conveying facility.